Low-voltage high-efficiency fluorescent signage, particularly exit sign

ABSTRACT

An &#34;exit&#34; sign lighting system comprising, in combination a housing having the word EXIT formed in an opening wall thereof, a translucent member in said opening, a gas discharge device, such as a fluorescent tube is driven from a source of a low-voltage, high-frequency square wave voltage having a pair of output terminals and an LC free circuit connecting the low-voltage, high-frequency square wave voltage to the gas discharge device to non-thermionically excite and illuminate the gas discharge device, and thereby illuminate the translucent member and the word EXIT. The low voltage is from about 2 volts to about 90 volts and the frequency is from about 75 kHz to about 3.5 MHz.

The present invention is related to my provisional application Ser. No.60/053,796 filed Jul. 25, 1997 entitled LOW-VOLTAGE, NON-THERMIONIC,BALLASTFREE FLUORESCENT LIGHT SYSTEM AND METHOD, which is incorporatedherein by reference.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION

Exit signs are located in theaters, public buildings, high-riseapartment buildings, and the like for purposes of guiding people safelyto exit stairways and exit doorways and the like from these suchstructures in times of emergency. Normally, they use incandescent lampswhich generate large amounts of heat thereby shortening the life of thelight source and requiring considerable maintenance and expense.Moreover, since these exit signs are located in buildings which requirethat they be on in times of emergency and highly visible, possiblythrough smoke and haze, they require a backup electrical power source inthe event of failure of the main power line, such as a conventional 110volt main. Such prior art systems also may require the alternative lampsor low-voltage lamps which turn on in the event of failure of the mainpower supply. See FIG. 1 and U.S. Pat. Nos. 5,611,163 and 5,526,251.There have been efforts to incorporate fluorescent lamps into exitsigns. See U.S. Pat. Nos. 4,587,600 and 4,650,265 as examples.

The object of the invention is to provide a new and improvedballastless, non-thermionic and starterless fluorescent exit sign whichworks on inducing oscillation on the gas contained in the tube at afrequency which is related to the type of gas to obtain maximumluminosity without the presence of a carrier, consumes little electricalenergy (2.6 watts) and which is dimmable without flickering regardlessof the level of luminosity and in which the light spectrum is constant.

Another object of the invention is to provide an improved exit signwhich is low in cost and low in energy consumption.

The exit sign of the present invention incorporates a ballast-free,starter-free, non-thermionic conventional fluorescent lamp or tubedriven by a high-frequency square wave driver circuit.

Another object of the invention is to provide a low voltage (under 85-90volts), non-thermionic, ballast-free, fluorescent lighting system forexit signs.

According to the invention at least one gas discharge lighting lamp ortube (which may be constituted by UV-responsive phosphor-coated envelopeconfining a gaseous discharge medium at a predetermined pressure betweena pair of electrodes) is mounted in an "exit" sign housing andnon-thermionically driven by a low-voltage square wave power supply. Thesquare wave power supply may incorporate a solid state switch which isoperated to generate a substantially square wave alternating currentwave at the lamp or tube electrodes such that the voltage supplied tothe electrodes reverses polarity more rapidly than the pattern ofelectron and ion density in the tube can shift so that electronsthroughout the length of the tube are continually accelerated and will,through several cycles of said square wave, create free electrons andions throughout the tube's volume, in steady state operation andilluminate the fluorescent lighting lamp. The frequency of oscillationis preferably related to the type of gas to obtain maximum luminositywithout the presence of a carrier. The current in the tube is minimaland no noticeable level of RFs are present, that is, there issubstantially no radio interference.

The oscillating transformer in the present invention provides a level ofluminosity which is a function of the voltage thereby making dimming ofthe fluorescent lamp possible without flickering (90% dimming)regardless of the level of luminosity. The band on the spectrum isconstant and reflects the initial reaction to the oscillation. Thesystem works in any type of gas filled envelope.

Thus, there is disclosed a sign lighting system comprising a housinghaving signage indicia in a wall thereof. A fluorescent gas dischargelamp is mounted inside the housing and a source of low-voltagehigh-frequency square wave voltage having a pair of output terminals andan LC-free circuit connecting the low-voltage, high-frequency, squarewave voltage to the fluorescent gas discharge lamp to non-thermionicallyexcite the fluorescent member and the indicia formed on the wall of thehousing.

In a preferred exit sign system, a 7.2 volt DC rechargeable battery isused. The battery backup has a battery charging circuit and uses a 7.2volt nicad rechargeable battery. The fluorescent tube is an FT6fluorescent tube with no starter or ballast and the filaments are notconnected to a source of heater current. The light output in such a lampis bright and the battery good for three hours (when only ninety minutesare required by federal regulations). The exit sign uses 2.6 watts ofenergy (in comparison to the standard sign on the market uses 50 watts).The display is green which corresponds to the new spec for LED equippedsigns in the market which are only red. The cost of manufacturing ismuch lower than the standard sign on the market.

In one preferred embodiment, the driver circuit of the present inventionincludes an oscillating transformer having a primary and secondarywinding with the primary winding center tapped and coupled to the toggleor gate electrode of a switching diode. A supply of direct current suchas a low-voltage battery is applied through a electrolytic filtercapacitor and a 1500 ohm resistor bypassed by a capacitor. A thirdcapacitor shunts the switching diode. The circuit operates to provide3.9 megahertz square waves output on the secondary at 1.4 volts to afluorescent tube such as FT6. An AC supply is rectified and used tosupply the driver circuit. A charging circuit for a battery is connectedto the AC supply. Upon failure of the AC supply, the batteryautomatically supplies DC voltage to the driver circuit.

DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the inventionwill become more apparent when considered with the followingspecification and accompanying drawings wherein:

FIG. 1 is a block diagram of prior art incandescent exit signs,

FIG. 2 is a block diagram having a driver circuit incorporating thepresent invention,

FIG. 3 is a detailed circuit diagram of the driver circuit of thepresent invention,

FIG. 4 is a diagrammatic illustration of a transformerless square waveinverter circuit of the present invention, and

FIG. 5 is a schematic isometric view of an exit sign and housingincorporating the invention.

DETAILED DESCRIPTION OF THE INVENTION

The system of the present invention uses a square wave AC invertercircuit to drive the electrodes of a fluorescent tube mounted in an exitsign. The square wave alternating current wave at the tube electrodes issuch as to reverse polarity more rapidly than the pattern of electronand ion density in the tube can shift so that electrons throughout thetube are continuously accelerated and will, through several cycles ofthe square wave create free electrons and ions throughout the gas tube'svolume, in steady state operation and illuminate the exit sign'sfluorescent lighting lamp. The frequency of oscillation can be relatedto the type of gas to obtain maximum luminosity without the presence ofa carrier. The current on the tube is minimal so when operating from thebattery, there is low drainage and long time of operation when there isa power outage, and there is no noticeable level of RF present so thereis little or no radio interference. The present invention uses anoscillation transformer, and the level of luminosity is a function ofthe voltage making dimming of the fluorescent lamp possible withoutflickering (90% dimming) regardless of the level of luminosity. The bandon the light spectrum is constant and reflects the initial reaction tothe oscillation. The system works in any type of gas-filled envelope.

Referring now to FIG. 2, a step-down transformer supplies AC voltage(120V) 26 to an inverter 10 which charges battery 11 coupled to analternating square wave driver circuit 12 which in turn supplies thehigh-frequency (3.9 megahertz at about 1.4 volts) alternating currentsquare wave to fluorescent tube 13 which emits light 14. The drivercircuit is shown in detail in FIG. 3. Switch 15 couples DC voltage (7.2volts) from battery 11 to the driver circuit 13. The driver circuitincludes an oscillation transformer T1 having a center tapped primaryhaving windings P1, P2 with the center tap connected to the gateelectrode of solid state switch or oscillating diode D1. The opposingends of oscillating diode D1 are connected to the upper and lower endsof the primary windings P1, P2 of transformer T1. A filter capacitor C1is connected across the 7.2 volt direct current input, and a filtercapacitor C3 is connected to coupling resistor R1. A shunt capacitor C2shunts the oscillating diode D1. The output to the fluorescent tube isabout 1.4 volts at 3.9 megahertz open circuit and 1.7 megahertz squarewave at the tube. Thus, the circuit has no ballast, no starter, nofilament current source, is non-thermionic and produces more light usingthe conventional fluorescent lamps and because it is non-thermionic issignificantly more efficient.

FIG. 3 illustrates a low-voltage square wave inverter circuit requiringa minimum of five components (the electrolytic filter capacitor C1 isdeemed to be a part of the DC power source or supply). Switch 15 couplesDC voltage (7.2 volts for example) from a battery to the low-voltagesquare wave inverter drive circuit resistor R1 can be a dimmer(intensity control) resistor. This driver circuit includes anoscillation transformer T1 having a center tapped CT primary windinghaving primary windings P1 and P2 with the center top CT connected togate electrode G of solid state switch D1. The opposing ends of switchD1 are connected to the upper and lower ends of the primary windings P1and P2. A capacitor C3 shunts the oscillating transistor/diode D1. Theexemplary circuit components are as follow:

    ______________________________________                                        Fluorescent tube  FT6                                                         Resistor R1                     1500 Ohms                                     Capacitor C1                   47UF 10 V Electrolytic                         Transistor diode 01                                                                              5609/6BC/ECB                                               Capacitor 31                   2A562K                                         Capacitor 32                   2A22K                                          ______________________________________                                    

The output to the fluorescent tube is about 1.4 volts RMS at 3.9 MHzopen circuit and 1.7 MHz, square wave at the tube. Thus, the system hasno ballast transformer, no thermionic heating of filaments, no startercircuit, and produces light in a more energy-efficient way.

FIG. 4 diagrammatically illustrates a transformerless square waveinverter circuit. Here, the positive (+) and negative (-) terminals of adirect current source are alternately connected to opposing electrodesof the fluorescent lamp(s). In this case, when switches S1 and S2 areclosed simultaneously or at the same time (preferably by the same signalfrom controller CONT, the positive terminal (+) is connected toelectrode 4-1 and the negative terminal (-) is connected directly toelectrode 4-2. When the switches S3 and S4 are simultaneously closed(and switches S1 and S4 are open) by controller CONT, the positiveterminal (+) is connected directly to lamp electrode 4-2 and thenegative terminal (-) is connected to fluorescent lamp electrode 4-1.Controller CONT can operate the switches in the range of about 75 kHz toabout 3.9 MHz and preferably operates the switches to cause the squarewave applied to lamp electrodes 4-1 and 4-2 to be at a frequency ofabout 100 kHz.

FIG. 5 illustrates an "exit" sign housing HO in which the word "exit" isformed in openings OP in a wall WA and a translucent panel member TPM,colored green or red, etc. so that when illuminated from inside theclosed housing HO by the fluorescent lamp which has been excited by thesquare wave driver circuit disclosed herein. The word "exit" or othersignage is illuminated.

While preferred embodiments of the invention have been shown anddescribed, it will be appreciated that other embodiments, adaptationsand modifications to the invention will be readily apparent to thoseskilled in the art.

I claim:
 1. A sign lighting system comprising, in combination a housinghaving an information indicia formed in one or more walls thereof, afluorescent gas discharge lamp means, a source of a low-voltage,high-frequency square wave voltage having a pair of output terminals andsubstantially LC free circuit connecting said low-voltage,high-frequency square wave voltage to said fluorescent gas dischargemeans to non-thermionically excite and illuminate said fluorescent gasdischarge lamp means, and thereby illuminate said information indicia.2. The sign lighting system defined in claim 1 wherein said low voltageis from about 2 volts to about 90 volts and the frequency is from about75 kHz to about 3.5 MHz.
 3. A sign having a housing with informationindicia thereon, the sign having a lighting system including afluorescent gas discharge lamp device mounted in said housing, a sourceof low-voltage, high-frequency, square wave AC voltage having outputterminals and a substantially LC-free circuit connecting said gasdischarge lamp device to said output terminals to excite and illuminatesaid fluorescent gas discharge lamp device to thereby illuminate saidinformation indicia.
 4. A sign as defined in claim 3 including a sourceof AC line current, a stepdown transformer connected to said source andhaving a low AC voltage output, a rectifier connected to said low ACvoltage output, a rechargeable storage battery connected to saidrectifier and means connecting said low voltage output to said circuitand said rechargeable battery.
 5. A sign having a housing withinformation indicia thereon, the sign having a lighting system forilluminating said information indicia including a fluorescent gasdischarge lamp device mounted in said housing, a circuit including asource of low-voltage, high-frequency, square wave alternating currentvoltage and means connecting said gas discharge lamp device to saidcircuit to excite and illuminate said fluorescent gas discharge lampdevice and thereby illuminate said information indicia.
 6. A sign asdefined in claim 5 including a source of AC line current, a stepdowntransformer connected to said source and having a low AC voltage output,a rectifier connected to said low AC voltage output, a rechargeablestorage battery connected to said rectifier and means connecting saidlow voltage output to said circuit and said rechargeable battery.
 7. Alow-voltage, high-efficiency, fluorescent signage comprising a housinghaving walls, sign in at least one of said walls and indicia adapted tobe illuminated from the rear, a fluorescent gas discharge lamp devicemounted in said housing, a source of low-voltage, high-frequency, squarewave AC voltage having output terminals and an LC-FREE CIRCUITconnecting said low gas discharge lamp device to said output terminalsto excite said fluorescent gas discharge lamp device and illuminate saidsign indicia.